1. Field of the Invention
The present invention relates generally to a redundant circuit for a semiconductor device. More particularly, it relates to a redundant circuit for a semiconductor device capable of controlling the operation of a high-voltage generator that has been already used in response to a determination whether or not a chip is normal.
2. Description of the Related Art
If any one of multiple microscopic cells, constituting a dynamic random access memory (DRAM) or synchronous memory device, fails, the DRAM cannot perform a normal function. This case employs the redundant structure which has an advantageous yield aspect by replacing the defective cell with an extra memory cell provided in the DRAM or synchronous memory device.
In the redundant structure, redundancy cells of a memory are arranged by sub-array blocks. In case of a 16M DRAM, extra row and column are provided in advance at every 256K cell array, and if one memory cell fails, the other (redundancy cell) will be available for circuit operation in the unit of row/column.
In other words, if the wafer process is completed, its internal circuit is programmed to change to an address signal of the redundancy cell. Accordingly, if there is an input of an address corresponding to the failed line during actual use, a selection is changed to an extra line. This program is characterized as an electric fuse technique by which a fuse is melted with overcurrent to be cut and a laser-beam technique by which a fuse is burned by laser beam.
If power is applied to a high-voltage generator provided in a normal chip (memory cell) and a repair chip, it is always actuated. Thus, if only the normal chip is operated, the unnecessary power loss occurs.
More specifically, in case of the normal chip, fuse blowing for repairs is not made, and a repair address enable pass is shut off. Even if a high-voltage generator relating to the repair address generation only maintains a lower voltage (about Vcc-Vt: the level of precharged voltage applied prior to actuating a charge pump at the time of applying the power thereto if a ring oscillator of the high voltage generator is disabled) than a high voltage (e.g. over 1.5 Vcc), there is no problem with the high-voltage generator in voltage. If the power is applied, the high-voltage generator maintains its operating state all the time, which causes unnecessary power consumption.